1. Technical Field
The present invention relates to a liquid droplet ejecting method and a liquid droplet ejecting apparatus.
2. Related Art
As an example of the liquid droplet ejecting apparatus, an ink jet printer which performs printing (recording) of an image by ejecting liquid droplets (ink droplets) onto various printing media such as paper, or a film, has been known. The ink jet printer alternately repeats a dot forming operation in which ink droplets are ejected from each nozzle, while moving (scanning) a head, in which a plurality of nozzles are formed, in a scanning direction with respect to a printing medium, and a transport operation in which the printing medium is moved (transported) in a transport direction which intersects the scanning direction, forms dots which are aligned in the scanning direction (dot column) in line in the transport direction, and forms an image on the printing medium.
In such an ink jet printer, as one method of further increasing a printing speed, a method of increasing the number of nozzles has been adopted. Specifically, in the method, a printing speed is increased by increasing the number of dots which is ejected in one scanning, by increasing the number of nozzles per head, or by aligning a plurality of heads. Forming of an image in a region with a width corresponding to a length of a column which is formed of a plurality of nozzles (plurality of heads) (band) is finished using one scanning, transporting of a printing medium in the transport direction is performed corresponding to the width, subsequently, and a band is formed by aligning an end portion of the band which is formed, and an end portion of a band which is formed by the subsequent scanning in the transport direction so that the end portions come into contact with each other. By repeating this process, an image is formed. It is possible to perform printing at a high speed using the method; however, in the method, there is a case in which a striped pattern (banding) occurs at a boundary of the band. This is caused by a variation in sending accuracy in the transport direction, a difference in ink ejecting properties at a switching portion of a nozzle column (variation in landing position of ink droplets, a variation in amount of ink droplets), or the like.
In JP-A-6-47925, as a method of suppressing deterioration in image quality due to the banding, a method in which a variation in ejecting properties or ejecting accuracy of an ejecting port is dispersed has been proposed. Specifically, as the simplest example, there is a method in which a part of dots in a lower end region of a band which is firstly formed, and a part of dots in an upper end region of a band which is subsequently formed are formed so as to overlap in the same region, by causing the lower end region of the band which is formed along with scanning of a head, and the upper end region of the band which is formed along with the subsequent scanning of the head to overlap. In addition, in JP-A-10-323978, a method in which a high quality image is formed using a plurality of nozzle columns has been proposed.
However, in a case in which an amount of ink droplets which are ejected is set to be small, and the number of dots for forming an image is increased in order to obtain a high definition image, there is a problem in that banding may occur due to a difference in timing at which ink droplets are ejected. Since a degree of dryness varies according to a passage of time after landing of ink droplets in plurality of adjacent dots which form an image, there is a difference in degree of bleeding, or a difference in shape on the surface as a result, due to a degree of dryness of surrounding ink droplets which previously landed and new ink droplets which land on the adjacent positions. For this reason, in a case of forming an image in a certain region, when a distribution of time interval in landing of a plurality of ink droplets for forming an image (respective pixels) is remarkably different from that in another adjacent region, there is a difference in degree of bleeding, or a difference in shape on the surface of the ink droplets, and as a result, a visually recognized unevenness (for example, uneven glossiness) occurs. In particular, in the upper end region or the lower end region of a printing medium, there is a case in which a region in which the distribution of ink droplet landing time is different is generated due to the necessity for performing a switching control of a head which is used, and as a result, banding occurs.